1. Field of Invention
The field of this invention is pedestal cranes, and particularly to a bearing assembly between the upper works of a pedestal crane assembly and the pedestal.
2. Description of the Related Art
Pedestal cranes include a revolving upper works mounted on a central pedestal support column or kingpost. The upper works typically comprise a swing column surrounding the kingpost, a turntable, the crane gantry, the operator cab and associated equipment. To prevent excessive wear between the upper works of the crane assembly and the kingpost as the upper works rotates about the pedestal of the crane, various bearing assemblies are employed. Commonly, a lower radial bearing assembly and an upper bearing system are utilized in a pedestal crane, with the upper bearing assembly including a thrust bearing for vertical loads and a radial bearing for lateral loads.
U.S. Pat. No. 4,184,600 to Goss et al. discloses a method for removing a bearing assembly disposed between a revolving turntable of a pedestal crane assembly and the pedestal. The bearing of the Goss et al. disclosure is removable. The kingpost described in the Goss et al. patent describes a typical kingpost upper end having a lateral surface engaged by a thrust bearing and a cylindrical structure having a side member engaged by radial bearings. The method includes activating a support member capable of co-acting with and between the revolving turntable of the pedestal crane assembly and the upper end of the pedestal, centering the revolving turntable about the support column with alignment means, removing a retainer plate capable of securing radial and thrust bearings in position, and thereafter withdrawing the bearings from the support column and revolving turntable to permit inspection and replacement thereof.
U.S. Pat. No. 5,328,040 to Morrow discloses a thrust-centering crane having an upper bearing assembly including discrete thrust and radial bearings.
A prior art crane constructed by Marathon LaTourneau includes an upper bearing assembly and a lower thrust bearing assembly. The upper bearing assembly comprises a sphere referred to as a pivot ball attached to an upper lateral surface of the pedestal support column. A closed-end, hollow cylinder pivot ball cap surrounds the pivot ball. Segments of bronze having an inner face shaped to conform to the ball cap and an outer face conforming to the interior of a closed-end, hollow cylinder surround the pivot ball. The upper crane assembly includes thrust and radial bearings. A disadvantage of the Marathon LaTourneau crane is stress concentration at the ball base interface with the lateral support surface, thereby limiting the load capacity of the crane. Other disadvantages include: (i) to change the upper bearing requires partial removal of the upper works; (ii) the upper bearing totally encases the spherical pin, which prohibits or substantially impairs visual inspection without removing the bearing, and (iii) the upper bearing design prevents through passage for services such as electric swivels and air swivels.